Ladle bottom

ABSTRACT

The present invention relates to a metallurgical ladle and more particularly to the bottom of the ladle having an outlet through which the molten metal can drain. An object of the present invention is to increase the efficiency of a ladle draining operation, including reducing the amount of discarded metal, avoiding the premature flow of slag through the outlet, and reducing the contamination of slag in the molten metal effluent. The ladle bottom comprises a plurality of terraces and flow channels, ultimately directing the stream of molten metal to an outlet of the ladle. The terraces are described as capturing slag and the channels permit molten metal to flow preferentially through the outlet.

FIELD OF THE INVENTION

This invention relates generally to refractory article and, moreparticularly, to a refractory shape used in the transfer of molten metalin a continuous casting operation.

BACKGROUND

A ladle is a vessel that is used to hold or transport a batch of liquidmetal during metallurgical operations. A layer of slag frequently coversthe top surface of the liquid metal, such as in the production of steel.When desired, the liquid metal may be drained from the ladle though anoutlet located in the ladle bottom. While draining, the metal will,desirably and advantageously, completely empty from the ladle withoutcontamination of the metal by slag. Contamination is undesirable and maycause difficulties in casting or refining operations as well as defectsin the intermediate or final metal products.

Slag contamination can occur from both floating and entrained slag. Slagis typically less dense than liquid metal and generally floats in aseparated layer on the surface of a quiescent batch of liquid metal.During the pouring of the liquid metal, slag can become entrained withinthe flowing stream. Entrainment is the presence of slag particles in themolten steel. Entrainment often occurs when turbulence disturbs theinterface between molten metal and slag. Such turbulence can causemolten metal and slag to mix. Under quiescent conditions, entrained slagwould eventually float to the surface; however, the turbulence ofcasting can maintain a substantial amount of entrained slag in themolten metal. Ideally, any solution to the problem of slag contaminationwould address both floating and entrained slag.

As the metal drains from the ladle, the floating slag approaches theoutlet and the likelihood of contamination of the metal stream by slagincreases. An operator will stop the pour when he detects slag in themolten metal stream exiting the ladle. The operator may even stop thepour prematurely to avoid slag in the ladle outflow. The slag and metalremaining in the ladle are discarded. Discarding metal decreases yield,which is costly and inefficient but, at the same time, is necessary toreduce slag contamination.

Various methods and articles exist to detect slag in the ladle or theladle outflow. Frequently, these methods require action by the operatorand include electronic and sonic detection devices that are placedinside and outside the ladle. For example, a detector placed in theladle can detect a drop in the level of molten metal by measuring achange in electrical resistivity when floating slag intersects thesubmerged detector. Similarly, sonic pulses can identify the presence ofslag in the ladle outflow. Both techniques only detect the presence ofslag and do not actively decrease the presence of slag in the outflow.

Prior art includes article designed to reduce the outflow of slag fromthe ladle. U.S. Pat. Nos. 4,746,102 and 5,879,616 teach ladle bottomshaving a small well immediately above the ladle outlet. Both patentsdescribe the well as preferentially collecting molten metal instead ofslag, thereby improving yield as the ladle empties. Unfortunately, thepatents only prevent floating slag from exiting the ladle. Entrainedslag is free to exit the ladle.

U.S. Pat. No. 5,196,051 describes a ladle bottom for reducing entrainedslag. The ladle bottom comprises means for entrapping slag before theslag reaches the ladle outlet. The means extend upwards from the ladlebottom and include elongated castellations that approach the outlet. Oneembodiment shows castellations radiating symmetrically from the outlet.The symmetrical castellations are described as reducing vortexing, whichleads to slag entrainment. Notably, the castellations are not describedas promoting a reduction of entrained slag already present in the moltenmetal.

Prior art does not teach a ladle bottom that simultaneously reduces theoutflow of both entrained slag and floating slag. A need remains for anarticle capable of capturing entrained slag and allowing molten metal toflow from a ladle before floating slag.

SUMMARY OF THE INVENTION

An object of the present invention is to increase the efficiency of aladle draining operation, including reducing the amount of discardedmetal, avoiding the premature flow of slag through the outlet, andreducing the contamination of slag in the molten metal effluent.

The present invention relates to a metallurgical ladle and moreparticularly to the bottom of the ladle having an outlet through whichthe molten metal can drain and a method to increase the fraction ofliquid metal that can be drained from the ladle through the outletwithout contamination by slag.

The invention includes a ladle bottom comprising a plurality of terracesand flow channels, ultimately directing the stream of molten metal to anoutlet of the ladle. The terraces and channels are in the surface of theladle bottom that is exposed to the liquid metal.

A plurality of uppermost terraces comprises generally horizontal facesthat are substantially separated by at least one flow channel comprisingsidewalls and a bottom face. The terraces permit entrained slag toprecipitate from the molten metal. The channel allows uncontaminatedliquid metal to flow to the outlet hole and drain from the ladle evenwhen the metal level is very low and the floating slag layer is closelyapproaching the outlet.

The flow channel may have a plurality of branches, which allow thecollection of liquid metal from regions of the ladle that are remotefrom the outlet. The flow channel then feeds the collected metal to theoutlet. In a preferred embodiment, the depth of the channel increases insteps towards the outlet and terminates in a deepest face surroundingthe outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a prior art ladle, including the ladlebottom and outlet.

FIG. 2 is perspective view of a prior art ladle bottom havingcastellations radiating from the outlet.

FIG. 3 is a perspective view of a ladle bottom of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a ladle 1 of the prior art having a bottom 2. The bottom 2comprises an inclined portion 3 and a vertical portion 4 adapted todirect molten metal in the ladle 1 to an outlet 5. The vertical portion4 creates a well 6 immediately above the outlet 5. Molten metal isdirected to the outlet 5 by the inclined portion 3, and collects in thewell 6 before any slag, which may be floating on the molten metal. Thewell 6 is described as increasing the amount of molten metal that canpass through the outlet 5 before floating slag contaminates the outflow.

FIG. 2 shows another ladle bottom 2 of the prior art having an inclinedsurface 3 directed toward the outlet 5. Molten metal, being heavier thanslag, is expected to reach the outlet 5 before any floating slag. Aplurality of castellations 21 rises from the inclined surface 3. Thecastellations are described as reducing vortexing, thereby decreasingthe likelihood slag will entrain in the molten metal. Less entrainedslag would presumably decrease the amount of slag in the outflow. Onlythe inclination of the bottom 2 deters floating slag from exiting theladle.

FIG. 3 shows one embodiment of a ladle bottom 2 of the presentinvention. Not shown are the walls of the ladle that would surround thebottom and extend upward from the ladle bottom 2 to contain the liquidmetal and slag. The ladle bottom includes an outlet 5, which is normallyat the low point of the ladle. The bottom 2 also comprises a pluralityof faces 31 and sidewalls 32 that are exposed to the liquid metal.Sidewalls 32 are preferably substantially vertical relative to the faces31. The sidewalls 32 may also be curved, chamfered, or otherwise shapedto permit head pressure on the flow above the outlet and decrease slagcontamination.

The faces 31 include a plurality of uppermost faces 31A, which aregenerally horizontal. In association with adjacent sidewalls 32, theuppermost faces define terraces. The terraces may be at differentheights relative to the outlet. The terraces may also vary in thicknessdepending on casting conditions, such as the type and grade of moltenmetal, use of gas purging, impact on the ladle bottom during fillingwith molten metal, expected erosion, etc.

The remaining faces 31 include at least one intermediate face 31B, atleast one sloping face 31C, and at least one outlet face 31D.Intermediate face 31B is higher above the outlet 5 than sloping face 31Cand outlet face 31D but at a lower level than uppermost faces 31A.Intermediate face 31B converges toward the sloping face 31C. Preferably,the intermediate face 31B is inclined toward sloping face 31C.

Sloping face 31C slopes upward from the outlet face 31D to intermediateface 31B, thereby defining an elevation drop from the intermediate face31B to the outlet face 31D. The inclination of the sloping face 31C isgreater than the average inclination of the intermediate face 31B, andcan vary from a gentle slope to a perpendicular drop depending onconditions. As the slope of the sloping face 31C approachesperpendicular, the combination of sloping face 31C, sidewalls 32 andoutlet face 31D may define a well around the outlet 5.

The outlet face 31D includes the outlet 5 and is preferably is shaped todirect molten metal toward the outlet 5. The outlet face 31D should bethe lowest face 31 to ensure a higher yield of molten metal outflowingfrom the ladle.

The sidewalls 32 and lower faces 31B-D form a flow channel 33. Thepresent embodiment shows a flow channel 33 having three branches 33A-C,which separate the uppermost faces 31A from one another. At least onebranch is an outlet branch 33C. The branches may each be at differentheights and, preferably, the outlet branch 33C including face 31D is thelowest.

During casting, both floating and entrained slag tend to settle onuppermost faces 31A as liquid metal drains into the flow channel 33. Anyremaining slag then tends to settle on the intermediate face 31B asmolten metal flows down the sloping face 31C , the outlet face D, andthrough the outlet. A sharply inclined sloping face 31C can define awell, which reduces contamination of the outflow by floating slag.

Terracing the ladle bottom while providing flow channels for liquidmetal permits the liquid metal to exit the outlet with reduced slagcontamination. The terraces and sidewalls, collect or trap slag whilepermitting molten metal to continue towards the outlet. This phenomenontakes advantage of the lower density of slag and its higher viscosity incomparison to liquid metal.

Slag movement toward the outlet is retarded by friction against theladle bottom. The present invention takes advantage of this fact bycreating a plurality of slag-entrapping features. For example, as theliquid metal and slag settle onto an uppermost terrace, the molten metalflows off the terrace into the channel, while the more viscous slag isstranded on the horizontal face. Successive terraces can further improveseparation of slag from the liquid metal until, at the outlet, theliquid metal is substantially free of slag contamination.

The invention anticipates various terrace configurations. Factorsinfluencing the choice of configuration include the type or grade ofliquid metal, the impact of the flow onto the ladle bottom, gas purgingelements, and the geometry of the ladle. The uppermost terrace may behigher, that is, thicker, or more or less numerous to accommodate moreenergetic flow, corrosive metals or ladle geometry.

Obviously, numerous modifications and variations of the presentinvention are possible. It is, therefore, to be understood that withinthe scope of the following claims, the invention may be practicedotherwise than as specifically described.

1-11. (canceled)
 12. A ladle bottom adapted for use in a ladle formolten metal applications, the ladle bottom comprising: a) a pluralityof lower faces including at least one outlet face defining an outlet andat least one sloping face inclined upwards from the outlet face towardsat least one intermediate face; b) a plurality of sidewalls extendingupward from the lower faces, thereby defining at least one flow channel;and c) a plurality of uppermost faces above the lower faces relative theoutlet and at least substantially separated by at least one flowchannel, whereby the uppermost faces are adapted to preferentiallycapture slag while the flow channel permits the molten metal to draintoward the outlet.
 13. The ladle bottom of claim 12, wherein the ladlebottom comprises at least three uppermost faces.
 14. The ladle bottom ofclaim 12, wherein the uppermost faces are substantially horizontal. 15.The ladle bottom of claim 12, wherein the uppermost faces are atdifferent heights relative to the outlet.
 16. The ladle bottom of claim12, wherein the intermediate face has an inclination towards the slopingface and the inclination is less than an inclination of the slopingface.
 17. The ladle bottom of claim 12, wherein the sloping face issubstantially vertical, and the sloping face and the sidewalls define awell around the outlet face.
 18. The ladle bottom of claim 12, whereinthe sidewalls are substantially perpendicular to the faces.
 19. Theladle bottom of claim 12, wherein the flow channel has a plurality ofbranches.
 20. The ladle bottom of claim 19, wherein the branches includeat least one feeder branch and an outlet branch, the feeder branch beinghigher above the outlet than the outlet branch.
 21. The ladle bottom ofclaim 19, wherein the feeder branch are is shallower than the outletbranch.
 22. A ladle bottom adapted for use in a ladle for molten metalapplications, the ladle bottom comprising: a) at least one outlet facedefining an outlet; b) at least one sloping face having a lower endinclined upwards from the outlet face and an upper end; c) at least oneintermediate face contacting the upper end of the sloping face; d) aplurality of sidewalls extending upward substantially perpendicular fromthe outlet face, sloping face and intermediate face, thereby defining atleast one flow channel including at least one feeder branch and at leastone outlet branch; and e) a plurality of uppermost faces above theintermediate face and at least substantially separated by the feederbranch, whereby the uppermost faces are adapted to preferentiallycapture slag while the feeder branch permits the molten metal to draintoward the outlet branch and the outlet.